This invention relates to wireless communications systems, including those using satellites, stratospheric platforms, and even terrestrial towers, and particularly to the downlink portions of such systems, which portions transmit signals from wireless platforms such as earth-orbiting satellites to earth-based receiving stations.
One form of satellite communications systems transmits a single stream of data packets from a satellite for reception by multiple receiving stations at different locations on the surface of the earth. Different receiving stations are differentiated by means of a destination user code embedded in a destination user identity field of each data packet. Each receiving station accepts only those packets having its user identity code.
A problem arises in that the received signal strength is not the same at all locations. Typically, the signal strength is some three to four decibels lower at the edge of the transmitted beam as compared to the signal strength at the center of the beam. Thus, the performance of receiving stations located toward the edge of the beam may be reduced to an unsatisfactory level.
A typical solution to this problem is to increase the power of the transmitted downlink beam to the highest level required by any of the receiving stations which, in this case, will normally be the level required by stations located near the edge of the transmitted beam. This, however increases the power consumption of the satellite transmitter. This, in turn, reduces the maximum data handling capability of the satellite.
The present invention provides a better solution to this problem. It enables marginal receiving stations to be adequately serviced without increasing the power used for transmissions to non-marginal receiving stations.